<!DOCTYPE html>
<html lang="zh-CN">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>算术运算符 + 用于把值加起来</title>
</head>

<body>
    <p>点击按钮计算 x 的值.</p>
    <button onclick="myFunction()">点击这里</button>
    <p id="demo"></p>
    <script>
        function myFunction() {
            y = 5;
            z = 2;
            x = y + z;
            document.getElementById("demo").innerHTML = x;
        }
    </script>
</body>

</html>